Conventional fixed winged aircraft are provided with a variety of aerodynamic control devices which include, for example, flaps, elevators, ailerons, trim tabs, and rudders. These control devices cooperatively operate to increase or decrease lift over a given localized aerodynamic control surface for achieving pitch, yaw and roll control of the aircraft. Such control devices are used in both traditional winged and modern stealthy aircraft designs. These control devices are typically rigid structures which are integrated into the edges of the wings or body (i.e., aerodynamic lifting surfaces) of the aircraft. The control devices are configured to deflect or rotate about an axis of rotation in a hinge-like fashion with respect to the attached aerodynamic lifting surfaces. Typically, such a control device is characterized as having at least one end which is perpendicularly or at least angularly disposed with respect to the axis of rotation. Operation of the control devices typically forms gaps and/or abrupt changes in surface contours at or about the control device ends.
It is contemplated that gaps, abrupt changes, or contour discontinuities occurring between the aerodynamic lifting surface and the attached control device are especially undesirable because they tend to increase aerodynamic drag and lessen the aerodynamic effectiveness of the control surface due to "leakage" at the end portions of the control device.
Prior art attempts to mitigate the formation of such surface discontinuities include U.S. Pat. No. 5,794,893 to Diller et al. and U.S. Pat. No. 5,222,699 to Albach et al. which contemplate use of surface skins which span across the lifting surface/control device gap to smooth the surface transition thereat. These surface skins are formed of an elastomeric material which have rods integrated therein for structural support. It is contemplated that such structural support is required as such surface skin are exposed to various air loads which can undesirably deform the elastomeric surface skins. These reinforcing rods are typically disposed in a spanwise direction and are mounted in large end ribs with either "fixed" or "guided" end conditions. As the control device rotates, these rods are deflected into an "S" shape. In any deflected position, these spanwise rods are required to beam a combination of air load and induced bending load to the end ribs. In the undeflected position, the rods must beam only the air load to the end ribs. Regardless, due to the "fixed" and/or "guided" end conditions, each spanwise rod produced a resultant shear load and bending moment at the end ribs. Due to the plurality of spanwise rods, these shear loads and bending moments must be summed and become the driving design requirement for the end ribs. The resultant rib becomes large and heavy, typically requiring the use of a dense, high strength metallic material, in order to prevent large deflections (vertical and twist) of the end rib and adjacent fixed wing structure.
Such a design results in several complications. First, it is desirable for aircraft structures to be relatively light weight. The weight impact due to the addition of large end ribs tend to lessen the overall performance enhancement provided by the use of the rod reinforced transitions. Second, the hinge moment for driving the control device tends to be severely increased. This results in reduced control device deflection rates, increased actuation size and power requirements, or a combination thereof. Third, such large and heavy end ribs are not typically compatible with advanced military airframe edge designs. Contemporary edge designs call for relatively low density edge members, typically of a composite, thin skinned, honeycomb construction. Heavy metallic ribs are not compatible with this design construction. Finally, the reinforcing rods may tend to suffer from having a limited useful life due to large cyclic defections of the control device.
It is therefore evident that there exists a need in the art for an improved system which mitigates the formation of gaps and abrupt surface contour changes occurring between an aerodynamic lifting surface and an attached control device. In addition, there exists a need for such improved system which mitigates high shear loads and bending moments at the attachment points of the lifting surface and the control device.